Carbon fiber reinforced polymer (CFRP) composites are fiber reinforced composite materials that use carbon fiber as a primary structural component. CFRP composites use thermosetting resins, such as epoxy, polyester, or vinyl ester. The polymer is impregnated or coated on a woven carbon fiber cloth to provide a lightweight and strong material compared to other materials such as steel and aluminum. Consequently, CFRP composites are used where strong, lightweight structural materials are advantageous, such as in the aircraft and aerospace industries.
When fabricating CFRP structures, it is necessary to bond CFRP components with adhesives. Since such structures may be used to support loads in aircraft and other vehicles, it is necessary to test the strength and integrity of the bonds of CFRP composite structures. It is also preferable to test the integrity of such bonds non-destructively, in view of the cost of CFRP structures, and if possible to test the integrity of the bonds at the jobsite.
Systems have been developed to nondestructively test the integrity of bonds formed within a composite structure. For example, a laser bond inspection device, or LBID, utilizes a laser that is directed at a polyvinylchloride (PVC) tape that has been adhesively attached to the surface of the composite structure at the site of the bond to be inspected. The energy from the laser ablates the tape, creating compression waves that travel through the composite structure to be reflected from an opposite surface of the structure as tension waves. The tension waves stress the bondline and the resultant surface motion of the composite structure is detected by a velocity interferometer system for any reflector (VISAR), which measures velocity on the surface of the bonded structure.
A disadvantage with such LBID systems is that they require a relatively large laser—on the order of 40-50 joules—to project laser energy to ablate the PVC tape to generate compression waves capable of testing the integrity of the bondline of the composite structure. Such large lasers may be difficult to move to a job site to inspect a structure, are relatively costly, and require relatively large amounts of power to operate.
Accordingly, there is a need for a non-destructive bond inspection system and method that is relatively compact, low cost, and requires less power than conventional LBID systems.